Comprehension STOP Use your dictionary to find out the meaning of the bold words below. Tsunami Wave


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A tsunami is a large ocean wave. It is one of the world’s most powerful and damaging natural forces. It can speed across the ocean as quick as lightning, swallowing up islands and wiping out coastal villages.


What causes a tsunami?


The word tsunami means ‘great harbour wave’ in Japanese. About four out of five tsunamis happen within the Ring Of Fire, a zone in the Pacific Ocean where earthquakes and volcanic eruptions frequently take place. If an earthquake lifts or drops part of the ocean floor, the water above rises and starts spreading across the ocean, causing a tsunami. Underwater landslides or volcanic eruptions can also move water and may lead to a tsunami.*


How big is a tsunami?


Out in the open ocean, tsunami waves are only about one metre high because the water is deep. However, as the water becomes shallow, the waves slow down and begin to grow. They can rise 35 metres or higher – that’s the same as a 10-floor block of flats! However, the scariest thing about a tsunami is its wavelength, as this determines how far inland it can travel.


How fast is a tsunami?


A normal wind wave travels at about 90 km/h, but a tsunami can race across the ocean at an incredible 970 km/h! Sometimes, before a tsunami hits, there is a huge vacuum effect, sucking water from harbours and beaches. People can see the ocean floor littered with flopping fish and other sea animals. Then a wave blasts onto the shore minutes later, then another and another for two hours or more. There may also be up to one hour between each wave.


Can you predict when a tsunami is coming?


To help save lives, scientists established the Pacific Tsunami Warning System, based in Hawaii in the USA. Its network of detectors can track quakes that may cause a tsunami. These waves can race from one side of the Pacific Ocean to the other in less than a day, so people need to be warned in time to head for higher ground.


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Unit 15 | Explanatory Text 2


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